1. Field of the Invention
The present invention relates to a field emitter, and more particularly to a cathode plate structure formed on a common plane.
2. Description of Prior Art
In recent years, flat panel display comes with the thin and light features, and its resolution and brightness are even better than those of traditional televisions, and thus flat panel displays are used extensively in the applications of different display sizes including the flat display panels as small as those for mobile phones or as large as those for outdoor billboards, and the applications of flat panel displays become increasingly popular in the market.
Various different types of flat panel displays are introduced constantly to the market, and liquid crystal display (LCD), plasma display panel (PDP), organic light emitting diode display (OLED) and field emission display (FED), particularly the field emission display (FED) become the mainstreams of flat panel displays. The principle of the field emission display (FED) primarily bombards an electron beam produced by an electron emission source of a cathode onto a fluorescent layer to produce light.
In general, a conventional field emission display of a triode structure includes an anode plate, a cathode plate, and a gate electrode layer between the anode and cathode plates, wherein the gate electrode layer provides an electric potential to attract electrons produced by the cathode plate, and the anode conductive layer provides a high potential to accelerate the kinetic energy of electrons and bombard electrons onto the anode plate to produce light.
Although the conventional structure provides a normal light emission for the field emission display, the gate electrode layer is designed and disposed directly between the cathode plate and the anode plate and proximate to the emitter of the cathode plate, and thus causing a more complicated manufacturing procedure of the cathode plate and incurring a higher manufacturing cost. To lower the cost and overcome the shortcomings of the aforementioned structure, another conventional cathode structure disposed on a common plane of the emitter and the gate electrode as disclosed in U.S. Pat. No. 6,891,320 was developed, and such patent made changes to the cathode structure that adopts a stacking method, and thus not only simplifying the manufacturing procedure, but also lowering the manufacturing cost.
The aforementioned design of forming the emitter and the gate electrode on a common plane structure of the cathode substrate has the advantages of lowering the cost and simplifying the manufacturing procedure, but it also affects the electric field of the electrons horizontally attracted from the emitter to the gate electrode. Since the vector of the electric field at the gate electrode surface affects the quantity and direction of the field emission electrons. With the same condition of electric potential, the larger the interval between the emitter and the gate electrode, the smaller is the intensity of the surface field of the emitter, and thus the efficiency of producing electrons by the emitter is reduced and the light emitting effect of the field emitter is affected directly.
Although the interval between the emitter and the gate electrode can be reduced to less than several microns (μm) by semiconductor fabrication processes, yet a high cost is incurred. Under the same condition of electric potential, the interval between the emitter and the gate electrode is too small, and the two electric fields interfere with each other, so that a portion of the free electrons discharged from the emitter are attracted by the gate electrode and cannot be accelerated to the anode, but the free electrons are moved towards the gate electrode instead, and thus causing an electric leak. If a thick film process is adopted, the manufacturing cost can be lowered, but the interval between the emitter and the gate electrode must be maintained above tens of microns (μm) due to the accuracy of the printed circuit board, or else a deformation caused by the planarity of the emitter and the gate electrode or the sintered material will result, and the emitter and the gate electrode will not function. To compensate the excessively large interval formed between the emitter and the gate electrode by the foregoing process, it is necessary to increase the electric potential of the anode plate to obtain a larger electric field of the anode plate with respect to the cathode plate, and thus regardless of which manufacturing process is adopted, there is a drawback of using the common plane structure of the cathode plate. The prior art definitely requires further improvements and feasible solutions.